Stimulation of proteolytic activity of boar sperm acrosin by divalent metal ions

The in-vitro proteolytic activity of boar sperm acrosin was stimulated by a series of monovalent and divalent metal ions. Equivalent concentrations of monovalent cations resulted in nearly identical increases in proteolytic activity, probably related to the increased ionic strength of the incubation medium. However, at concentrations of monovalent cations that resulted in a 2- to 3-fold stimulation of proteolysis of Azocoll, divalent metal ions caused a 24-(magnesium) to 46-(calcium) fold increase in proteolytic activity. We suggest that the divalent metal ion binds to acrosin and thus increases the proteolytic activity of acrosin to an extent greater than that due to the increased ionic strength of the incubation medium.